The invention relates to aligning images of a projection system, such as a liquid crystal display (LCD) projection system, for example.
Referring to FIG. 1, a reflective liquid crystal display (LCD) projection system 5 typically includes an LCD display panel (LCD display panels 22, 24 and 26, as examples) for each primary color that is projected onto a screen 10. In this manner, for a red-green-blue (RGB) color space, the projection system 5 may include an LCD display panel 22 that is associated with the red color band, an LCD display panel 24 that is associated with the green color band and an LCD display panel 26 that is associated with the blue color band. Each of the LCD panels 22, 24 and 26 modulates light from a light source 30 to form red, green and blue images, respectively, that add together to form a composite color image on the screen 10. To accomplish this, each LCD display panel 22, 24 or 26 receives electrical signals that indicate the corresponding modulated beam image to be formed.
More particularly, the projection system 5 may include a beam splitter 14 that directs a substantially collimated white beam 11 of light (provided by the light source 30) to optics that separate the white beam 11 into red 13, blue 17 and green 21 beams. In this manner, the white beam 11 may be directed to a red dichroic mirror 18 that reflects the red beam 13 toward the LCD panel 22 that, in turn, modulates the red beam 13. The blue beam 17 passes through the red dichroic mirror 18 to a blue dichroic mirror 20 that reflects the blue beam 17 toward the LCD display panel 26 for modulation. The green beam 21 passes through the red 18 and blue 20 dichroic mirrors for modulation by the LCD display panel 24.
For reflective LCD display panels, each LCD display panel 22, 26 and 24 modulates the incident beams, and reflects the modulated beams 15, 19 and 23, respectively, so that the modulated beams 15, 19 and 23 return along the paths described above to the beam splitter 14. The beam splitter 14, in turn, directs the modulated beams 15, 19 and 23 through projection optics, such as a lens 12, to form modulated beam images that ideally overlap and combine to form the composite image on the screen 10.
However, for purposes of forming a correct composite image on the screen 10, the corresponding pixels of the modulated beam images may need to align with each other. For example, a pixel of the composite image at location (0,0) may be formed from the superposition of a pixel at location (0,0) of the modulated red beam image, a pixel at location (0,0) of the modulated green beam image and a pixel at location (0,0) of the modulated blue beam image. Without this alignment, the color of the pixel at location (0,0) may be incorrect, or the color may vary across the pixel.
At the time of manufacture of the system 5, the LCD display panels 22, 24 and 26 typically are mounted with sufficient accuracy to align the pixels of the modulated beam images. One way to accomplish this is to approximate the correct position of the LCD display panels 22, 24 and 26 and thereafter use the LCD display panels 22, 24 and 26 to attempt to form a white rectangular composite image onto the screen 10. If the LCD panels 22, 24 and 26 are not properly aligned, then red 42, green 44 and/or blue 46 color borders may be detected around the perimeter of a white image 40 that is formed on the screen 10, as depicted in FIG. 2. However, when the LCD panels 22, 24 and 26 are properly aligned, the color borders 42, 44 and 46 do not appear, and an enlarged white image 40 appears on the screen 10, as depicted in FIG. 3.
Unfortunately, conventional techniques that are used to align the LCD display panels 22, 24 and 26 may consume a considerable amount of time in the manufacture of the projection system 5. Furthermore, such factors as aging and thermal drift may cause the LCD displays panels 22, 24 and 26 to fall out of alignment during the lifetime of the projection system 5.
Thus, there is a continuing need to address one or more of the problems stated above.